This invention relates to a compound which is useful as a catalyst for an asymmetric Michael reaction and to a method of preparing a compound by means of a Michael addition reaction.
In recent years, the catalytic asymmetric Michael addition reaction promoted by chiral metal complexes has been recognised as an efficient method for performing enantioselective carbon-carbon bond formation reactions. Herein, a Michael addition reaction is a reaction between an enolate ion, formed from e.g. a ketone or xcex2-dicarbonyl compound and an xcex1, xcex2-unsaturated carbonyl compound, e.g. an enone. Although efficient catalytic asymmetric Michael reactions have been performed, there is still a need for improvements in terms of the range of starting materials with which the catalysts are active and stability of the catalyst. For example, aluminium bis(naphthoxide) may be applied as a catalyst only in reactions employing cyclic enones and is moisture sensitive (see Shibasaki et al, J. Org. Chem., 1998, 63, 7547).
In addition, the development of efficient methods to facilitate the recovery and reuse of asymmetric catalysts remains an important goal in organic chemistry. Intensive efforts have been devoted to develop soluble and insoluble polymer-supported asymmetric catalysts (see for example Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds., Springer: N.Y. 1999, Chapter 38). However the techniques employed often result in lower enantioselectivities or efficiencies than non-polymer-supported catalysts. Also, because of the difficulties associated with their recovery only a few reusable non-polymer-supported homogeneous asymmetric catalysts suitable for, e.g. Michael reactions, have been developed (for examples see Martinez et al, J. Am. Chem. Soc., 1995, 117, 5897; Tokunga et al, Science, 1997, 277, 936). Furthermore, reusable asymmetric Lewis acid catalysts are generally recognised as having a high sensitivity to moisture. Therefore, an increasingly important objective within this area is the development of highly stable asymmetric Lewis acid catalysts that can be recovered and reused.
Recent developments in ligand technology have seen the development of an oxygen-containing linked BINOL, which has the following structure; 
The ligand is chiral and possesses two chiral centres due to the tilting of the naphthoxy moieties relative to each other. The ligand may therefore be described as (R,R), (S,S) or (R,S). The (R,R) form of the linked BINOL has been used to effectively stabilize a Gaxe2x80x94Li complex against ligand exchange with a nucleophile under reaction conditions (see Shibasaki et al, J. Am. Chem. Soc., 2000, 122, 2252) but the group XIII metal complexes such as Al and Ga complexes have poor stability and so there is a desire to provide stable, storable and reusable homogeneous catalyst for the asymmetric Michael addition reaction.
We have found that lanthanum is an efficient Lewis acidic centre for the preparation of a novel, stable, storable and reusable catalyst.
It is an object of the present invention to provide a catalyst composition comprising a lanthanum-linked BINOL complex selected from the list consisting of;
(i) an unsubstituted lanthanum-linked BINOL complex of general formula (I), and
(ii) a substituted lanthanum-linked BINOL complex of general formula (I), wherein at least one of the hydrogen atoms on at least one of the aromatic rings of the complex is substituted with a substituting group. 
It is another object of this invention to provide the use of a lanthanum-linked BINOL complex of general formula (I) as a catalyst for a Michael addition reaction.
It is another object of this invention to provide a method of performing a Michael addition reaction comprising reacting a compound that forms an enolate ion and a xcex1, xcex2-unsaturated carbonyl compound in the presence of a catalyst composition comprising a lanthanum-linked BINOL complex of general formula (I).